The disclosure of Japanese Patent Application No. 2001-099764 filed on Mar. 30, 2001 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates generally to a vibration damping device installed in a various kinds of vibrative members in order to reduce vibrations excited in these vibrative members, and more particularly to such a vibration damping device that is novel in construction and that is suitably applicable as a vibration damping device for use on an automotive vehicle for damping vibrations excited in suspension arms, sub flames, body panels, mounting brackets, and vibrative members used in an engine unit and an exhaustion system.
2. Description of the Related Art
As examples of vibration damping means for damping or reducing vibration excited in various kinds of vibrative members, there are known (a) a mass damper in which a mass member is fixed to a vibrative member, (b) a dynamic damper in which a mass member is supported by and connected to the vibrative member via a spring member and (c) a damping material that is a sheet-shaped elastic member and secured to the vibrative member. However, these conventional devices suffer from various potential problems. For example, (a) the mass damper and (b) the dynamic damper both require a relatively large mass of the mass member, and exhibit a vibration damping effect only to a limited frequency range. (c) The damping material suffers from difficulty in stably exhibiting a desired damping effect, since the damping effect of the damping material is prone to vary depending upon the ambient temperature.
The present assignee has been disclosed in International Publication WO 00/14429 a novel vibration damper for use on an automotive vehicle, which includes a housing member fixed to the vibrative member, and an independent mass member that is housed in the housing member with a spacing therebetween, without being bonded to the housing member, so that the independent mass member is displaceable or movable relative to the housing member, while being independent of the housing member. In the disclosed vibration damper, the independent mass member comes into impact on or abutting contact with the housing member with elastic abutting surfaces, upon application of a vibrational load to the damper, whereby the vibration excited in the vibrative member is effectively reduced or absorbed. The proposed vibration damper is capable of exhibiting a high damping effect over a sufficiently wide frequency range of frequency of input vibrations, while having a relatively small weight in comparison with the conventional mass damper and dynamic damper.
The present invention has been developed by an extensive study of a vibration damper for use on an automotive vehicle disclosed in the above-indicated International Publication WO 00/14429. It is therefore an object of this invention to provide an improved vibration damping device capable of exhibiting a further improved vibration damping effect, in comparison with the vibration damper disclosed in the International Publication WO 00/14429.
The above and/or optional objects of this invention may be attained according to at least one of the following modes of the invention. Each of these modes of the invention is numbered like the appended claims and depending from the other mode or modes, where appropriate, to indicate possible combinations of elements or technical features of the invention. It is to be understood that the principle of the invention is not limited to these modes of the invention and combinations of the technical features, but may otherwise be recognized based on the teachings of the present invention disclosed in the entire specification and drawings or that may be recognized by those skilled in the art in the light of the present disclosure in its entirety.
(1) A vibration-damping device for damping vibrations of a vibrative member, comprising: (a) an abutting member adapted to be fixedly disposed in the vibrative member and having an abutting surface; and (b) an independent mass member disposed in relation to the abutting member such that the independent mass member is independently displaceable relative to the abutting member without being adhesive to the abutting member, the independent mass member having an abutting surface that comes into abutting contact directly and elastically with the abutting surface of the abutting member, wherein at least one of the abutting surfaces of the abutting member and the independent mass member is provided with a flock coating.
In the vibration damping device constructed according to this mode of the present invention, a vibrational load applied from the vibrative member to the vibration damping device causes a displacement of the independent mass member relative to the vibrative member. As a result, the independent mass member comes into impact on (abutting contact with) the abutting member, whereby the vibration-damping device can exhibit an excellent vibration damping effect as a result of the impact of the independent mass member on the abutting member.
Further, the independent mass member is displaced relative to the abutting member due to the vibrational load applied to the vibration damping device, and comes into abutting contact with the abutting member at their abutting surfaces at least one of which is provided with the flock coating. This enables the vibration-damping device to exhibit a higher damping characteristic in comparison with the case where the abutting surface is composed of a rubber elastic body or elastomer.
This abutting contact of the independent mass member with the abutting member via the flocked abutting surface or surfaces allows the vibration damping device to exhibit an excellent damping effect on the basis of the impact (abutting contact) of the independent mass member on the abutting member, without needing a significant increase of the mass of the independent mass member, with respect to low frequency vibrations. For this reason, the vibration damping device of this mode of the invention can exhibit a high damping effect with respect to vibrations excited in the vehicle whose frequencies ranging from about 10 Hz to about 100 Hz, for example.
The technical reasons for the above-described significant improve in the damping characteristics of the present vibration damping device owing to the use of the flocked abutting surface has not yet been revealed sufficiently. Although it is not an object of the invention to clarify this technical reason, it might be assumed that the flock coating provided on at least one of the abutting surfaces of the abutting member and the independent mass member allows the abutting and independent mass members to come into abutting contact with each other, while remarkably exhibiting a non-linear raise or increase of the spring constant generated between the abutting surfaces of the abutting member and the independent mass member.
A further extensive study of the present vibration damping device conducted by the present inventors reveals that the vibration damping device constructed according to this mode (1) of the invention permits that when the vibration damping device subjected to the vibration excited in the vibrative member, the independent mass member comes into impact on or abutting contact with the abutting member, while permitting the independent mass member to exhibit an amplitude magnification of not smaller than one with respect to the abutting member. This arrangement allows the independent mass member to impact on and rebound from the abutting member repeatedly in an easier manner, resulting in a bouncing displacement of the independent mass member relative to the abutting member with high efficiency. Therefore, the present vibration-damping device is able to provide the bouncing displacement of the independent mass member relative to the abutting member, if an acceleration of the vibration excited in the vibrative member is not greater than 1G (gravitational acceleration). For this reason, the vibration-damping device of this mode of the invention is capable of exhibiting an excellent vibration damping effect with respect to vibrations having a relatively small energy such as vibrations excited in the automotive vehicle, on the basis of the impact or abutting contact of the independent mass member on or with the abutting member. It has also been revealed that since the presence of the flock coating provided on the abutting surface or surfaces assures the non-leaner raise of the spring constant generated between the abutting surfaces of the abutting member and the independent mass member upon abutting contact of these members, the present vibration damping device does not need the independent mass member to completely rebound from or move away from the abutting member, for exhibiting a sufficiently high damping effect that is same as a damping effect obtained when the independent mass member completely rebound from the abutting member.
(2) A vibration-damping device according to the above-indicated mode (1) of the invention, wherein the abutting member comprises a hollow housing member adapted to be fixedly disposed in the vibrative member and including a storage space in which the independent mass member is housed. In this mode of the invention, the abutting member is formed by the hollow housing member, making it possible to stably install the present vibration-damping device in the vibrative member, regardless of the configurations or other factors of the vibrative member.
The housing member may be integrally formed with the vibrative member by effectively utilizing a vibrative member to partially or entirely form the housing member, or alternatively, the housing member may be formed independently of the vibrative member, and then is integrally fixed to the vibrative member by welding, bolts or other fastening means. The number of independent mass member housed in the housing member is desirably determined taking into account the size or shape of the storage space of the housing member, the size of the vibrative member, the level of the vibration excited in the vibrative member. The single storage space may house a single or a plurality of the independent mass member or members. Where a plurality of independent mass members are adopted, these plurality of independent mass members may have a uniform configuration or different configurations in both cases where these plurality of independent mass members are housed in a single storage space and where these plurality of independent mass members are a plurality of storage spaces, respectively. The housing member and the storage space may have a variety of configurations and sizes, without any limitation. For instance, the housing member and the storage space may be selected from a spherical shape, a circular shape in cross section, a rectangular shape in cross section, a polygonal shape in cross section, or the like, while taking into account the configuration of the vibrative member and a space usable for installing the vibration damping device. The configuration of the independent mass member may be suitably desirably selected depending upon the configuration of the storage space, among a variety of configurations including a solid or a hollow spherical shape, a rod shape a plate-like shape.
(3) A vibration-damping device according to the above-indicated mode (1) of the invention, wherein the abutting member comprises a longitudinal rod shaped member adapted to be fixedly disposed in the vibrative member, while the independent mass member comprises an annular or cylindrical member disposed radially outwardly of the rod shaped member. In this mode of the invention, the use of the longitudinal rod shaped member makes it easy to provide the abutting surface of the abutting member to be abutting contact with the independent mass member with simple construction. Further, the independent mass member comes into abutting contact with the abutting member at its inner circumferential surface, permitting the independent mass member to enlarge its outside dimension, in comparison with the case where the independent mass member is housed in the storage space of the housing member and comes into abutting contact with the abutting member at its outer circumferential surface. Therefore, the vibration-damping device of this mode of the invention is effective to obtain a mass of the independent mass member.
The longitudinal rod shaped member may be solid or alternatively be hollow. The traverse cross sectional shape of the rod shaped member is not particularly limited but may be selected from a circular shape, an ellipsoidal shape, a polygonal shape or the like, for example. The longitudinal rod shaped member may be provided with a stopper member that functions to limit an amount of axial displacement of the independent mass member relative to the rod shaped member for thereby preventing a disengagement of the independent mass member from the rod shaped member. This mode of the invention may be effectively adoptable when the vibrative member itself has a longitudinal rod shaped member. In this case, the vibration damping device of the present invention can be made simple in construction, in comparison with the case where the vibration damping device includes a housing member that houses the independent mass member and fixed to the vibrative member.
(4) A vibration-damping device according to any one of the above-indicated modes (1)-(3), wherein the at least one abutting surfaces provided with the flock coating comprises a metallic base. In this mode of the invention, the abutting surface comprises the metallic base provided with the flock coating permits the abutting member and the independent mass member to impact on each other with the non-linear raise of the spring constant generated between abutting surfaces of the abutting member and the independent mass member in a more efficient manner. According to this mode of the invention, the independent mass member and the abutting member may be formed of a metallic base only at their abutting surfaces or alternatively in their entirety. In particular, to form independent mass member out of the metallic base is effective to obtain a sufficiently large mass thereof. The flock coating may be formed on the surface of the metallic base according to know flocking methods. Preferably, the metallic base is initially subjected to a degreasing and conversion treatments. Subsequently, an adhesive layer is applied on the surface of the metallic base by dipping, spraying or the like. Finally, a multiplicity of suitable piles are planted to the outer surface of the metallic base according to a variety of flocking method including an electrostatic flocking.
(5) A vibration-damping device according to any one of the above-indicated modes (1)-(4), wherein the independent mass member has an outer circumferential surface serving as the abutting surface thereof, and having a spherical or cylindrical shape with a circular cross sectional shape, and the flock coating is provided on the outer circumferential surface of the independent mass member. In this arrangement, the abutting surface of the independent mass member is provided with the flock coating and has the spherical or cylindrical shape with the circular cross section, facilitating rotation of the independent mass member. As a result, the independent mass member is likely to change its abutting portion frequently, thereby effectively preventing a local abrasion or deterioration of the flock coating and a resultant change of the vibration characteristics of the vibration-damping device. In addition, since the independent mass member has the spherical or cylindrical shape with the circular cross section, the independent mass member is able to come into abutting contact with the abutting member at its abutting surface whose area is effectively reduced. This arrangement effectively lowers resistance to the displacement of the independent mass member, such as friction upon the abutting contact of the independent mass member with the abutting member, effectively exciting the bouncing displacement of the independent mass member with respect to the abutting member upon application of vibration to the vibration-damping device. Thus, the vibration-damping device of this mode of the invention can exhibit an excellent vibration damping effect on the basis of the impact or abutting contact of the independent mass member on or with the abutting member with a further improved efficiency.
(6) A vibration-damping device according to any one of the above-indicated modes (1)-(5) of the invention, wherein the flock coating provided on the at least one of the abutting surfaces of the abutting member and the independent mass member is formed by using a multiplicity of piles each made of a synthetic resin material and having a thickness of 0.3-3.0 denier and a length of 0.1-3.0 mm. This arrangement makes it possible to ensure a suitable spring characteristic at the abutting portion between the independent mass member and the abutting member for providing a desired vibration damping effect.
(7) A vibration-damping device according to any one of the above-indicated modes (1)-(6) of the invention, wherein the at least one of the abutting surfaces of the abutting member and the independent mass member is provided with the flock coating at one part thereof and with a thin-elastic body layer whose thickness is made smaller than the length of said each pile at an other part thereof. In this mode of the invention, the vibration damping characteristics of the vibration damping device, e.g., a peak of a resonance-like damping effect of the vibration damping device on the basis of the abutting contact of the independent mass member with the abutting member can be tuned by changing an area of the part of the abutting surface to which the flock coating is provided. In addition, the other part of the abutting surface is provided with the thin-elastic body layer, thus almost eliminating a problem of undesirable impact noises generated upon abutting contact of the independent mass member and the abutting member with each other.
(8) A vibration-damping device according to any one of the above-indicated modes (1)-(7), wherein the independent mass member has a mass within a range of 5-500 g in a single form thereof. Namely, if the mass of the independent mass member is set to 500 g or smaller, more preferably 100 g or smaller, the independent mass member can exhibit a relatively low spring characteristic owing to the flock coating, and is less likely to suffer from a problem of fatigue of the flock coating provided on the abutting surface thereof. Moreover, the independent mass member is likely to excite its bouncing displacement upon application of the vibrational load to the vibration-damping device in easier and more efficient manner. If the mass of the independent mass member is set to 10 g or more, more preferably 50 g or more, the vibration-damping device is able to effectively exhibit a desired damping effect on the basis of the abutting contact of the independent mass member with the abutting member in a more effective manner.
(9) A vibration-damping device according to any one of the above-indicated modes (1)-(8), wherein an overall mass of the independent mass member is held within a range of 2-10% of an overall mass of the vibrative member. Namely, if the overall mass of the independent mass member is smaller than 2% of the overall mass of the vibrative member, the vibration-damping device may become insufficient to exhibit an intended damping effect, and if the overall mass of the independent mass member is larger than 10% of the overall mass of the vibrative member, the vibration-damping device may suffer from a problem of increase in the overall weight of the device. In this respect, when the vibration-damping device includes a plurality of independent mass members, the combined mass of the plurality of independent mass members is interpreted to mean the above-indicated overall mass of the independent mass member, so that the combined mass of the plurality of independent mass member is arranged to be held within a range of 2-10% of the overall mass of the vibrative member, preferably.
(10) A vibration-damping device according to any one of the above-indicated modes (1)-(9) of the invention, wherein the abutting member includes two of the abutting surfaces which are opposed to each other in a vibration input direction with the independent mass member interposed therebetween such that the independent mass member is reciprocatory displaceable between the two abutting surfaces by a distance within a range of 0.1-1.6 mm so that the independent mass member comes into abutting contact with the two abutting surfaces of the abutting member located on opposite sides of the independent mass member in the vibration input direction. In this mode of the invention, the distance of the reciprocatory displacement of the independent mass member is set to such a small range, so that the independent mass member is likely to come into abutting contact with the abutting member on the opposite sides thereof in the vibration input direction, even if the input vibration has a relatively small amplitude like vibrations excited in the vehicle. Thus, the vibration-damping device can exhibit an excellent vibration damping effect with respect to vibrations excited in the vehicle.
(11) A vibration-damping device according to any one of the above-indicated modes (1)-(10) of the invention, wherein the abutting member and the independent mass member are formed of a rigid material having a modulus of elasticity of not smaller than 5xc3x97103 MPa, and the at least one of the abutting surfaces is provided with the flock coating. This arrangement enables the vibration-damping device to exhibit a desired vibration damping effect on the basis of the repeated impact (abutting contact) of the independent mass member on (with) the abutting member in a further efficient manner. For instance, the abutting member and the independent mass member may be formed of a hard synthetic resin material having a modulus of elasticity within a range of 5xc3x97103-5xc3x97104. This arrangement may be effective to reduce the impact noise generated upon impact of the independent mass member on the abutting member, and to improve vibration-damping effect of the vibration-damping device with respect to vibration in a low frequency band. In order to ensure a high damping effect of the vibration damping device with respect to intermediate and high frequency vibrations, an iron or a rigid material having a modulus of elasticity of not smaller than 5xc3x97104 MPa is preferably adopted for a material for forming the abutting member and the independent mass member.